A Deeper Look at the Process of Centrifugal Casting, What it Is, and the Benefits of the Process
The primary point of centrifugal casting is to introduce to the public the process by which manufacturing firms make thin-walled cylinders. This casting technique controls the amount of metal and crystal structure used. A centrifugal casing technique is proper when the manufacturer wants the piece to look symmetrical in a rounded form when preparing stock materials in standard machining sizes.
Centrifugal casting is required for product durability in products with high risk for reliability, such as jet engine compressor cases, military products, and hydro wear rings. Centrifugal casting is the choice process. Additionally, this process offers cost-effectiveness.
Materials Used in Producing Casts
The primary materials used in centrifugal casting include concrete, glass, metal, and pottery. Therefore, cylinders use steel, iron, stainless steel, copper, magnesium, and nickel alloys. The process can use two materials that can be combined by introducing a second material, such as iron and cement, where cement coats the interior of a cast iron pipe.
The Technique of Centrifugal Casting
The insides of a cast mold must be rotated constantly at a high speed while a permanent mold repeatedly turns at a high rate; molten metal, for example, is poured into the cast. The constant rotation of the casting mold causes the molten metal to cover the inside walls of the form, and as it cools, it hardens together. Centrifugal casting removes the need for cores.
All materials contain impurities, no matter what the manufacturer uses in this process. The casting of these forms uses a casting with fine grain. The outer sections are made up of a fine-grain coating. Because cooling occurs rapidly on the surface, the impurities gradually move towards the inside. During machining, these impurities the manufacturer machines these away.
Types of Casing Machines
There are two types of casing machines: vertical and horizontal.
When long, thin cylinders are preferred, this process requires a long steel casting mold spun at high speeds while horizontal to offset gravitational forces.
The mold has covers at each end to contain the molten metal. As the mold is rotated at a high speed, a pour funnel is used to apply more molten metal into the mold until it reaches a specified weight. The amount of metal running inside determines the I.D. size.
These cylinders are preferred for rings and bearings. Some have O.D. shaping rotating about the vertical axis. O.D. shaping is achieved by adding sand, ceramic, or graphite to the die. This method reduces the post-processing.
These casing molds are made in any thickness, diameter, or length. The casting height is less than twice the width. Depending on the purpose, this same mold can make different thicknesses.
Due to centrifugal casting, the technique provides the most excellent properties because of the grain structure caused by the fast rotating action of the centrifuge during the casting process.
Centrifugal casting can produce shapes up to 20 feet in diameter and 49 feet in length. This process allows the wall thicknesses to be from 0.098 to 4.921 inches.
When centrifugal casting is used inside a vacuum, it controls the exposure to the atmosphere, such as oxygen, because some alloys like nickel-cobalt react to oxygen.
Casting in a vacuum,
- Controls exposure to the atmosphere
- Achieves high metal integrity
- Achieves directional solidification
- No porosity
- Net-shaping takes place
- Produces high-reliability of product
Using Glass Material/Spin Casting
The glass industry calls this technique spinning because the rapid spinning of the material presses the molten glass against the inner wall, where it hardens.
During the cooling process, taking 16 hours to 72 hours, the impurities are pushed inward. Glass material answers the need for missile nose cones, television tubes, mirrors, marbles, and large telescopes. Using molten glass reduces the need for further grinding.
A peripheral mold and back pattern on a turntable are used within a furnace, eliminating the need for pouring glass into a mold. The material is heated and slowly spun until the glass solidifies. It takes months for the cooling process.
A permanent mold holds molten metal while rotating at consistently high speeds of up to 3000 rpm. As the mold turns, the metal spreads over the inside wall, covering the wall. As the metal cools, it hardens.
Because of the rapid cooling on the surface, the casting is fine-grained with a fine-grained outer diameter. During the cooling process, impurities of the metal move inward and are easily machined away following casting.
Summary of the Benefits of Centrifugal Casting and When This Is Required
This technique forms cylinders and shapes with long axis parallel to the ground. Forms are not standing during the process because the material can spread more evenly over the inward walls due to gravity. Cylinders with thin walls are difficult to cast any other way.
This centrifugal casting process is helpful in the manufacture of disk and cylinder-shaped products, for example, carriage wheels and machine fittings. It makes a difference in the grain flow and balance of these products that require durability and utility.
Products requiring a non-circular shape can also be cast; however, the form must be constant in radius. Centrifugal casting is necessary for the following.
- Products that rotate on an axis
- When material properties prove inadequate
- When other casting processes cause the centerline to shrink
- I.D. features are limited
- Need for uniform grain structure
- Dimensional integrity required
- Required alloy does not work for other processes
- Answers the need for large parts up to 135,000 or more pounds